- Correctness. It's still possible to generate bad XML. Especially in
safe mode, checks on processing instructions, comments and DOCTYPE
declarations should be rigorously matched against the spec.
- Control over presentation. How much is too much? Entities vs. CDATA,
placement of namespace declarations, whitespace. How much control
should the user be given?
- Performance. Reducing the use of closures may speed things up, and
benchmarking would show whether or not it's worth it.